The art of solid phase welding or pressure welding, particularly as applied to the joining of adjacent pipe ends, is described and disclosed in U.S. Pat. No. Re. 28,190 of Oct. 8, 1974. In said patent, there is provided a method of solid phase welding of pipes wherein two horizontally disposed pipes are positioned in axial alignment with their adjacent ends placed in contiguous relation, and axial upsetting pressure is applied to the abutting ends while heat is applied thereto. The heat is applied externally of the pipe, preferably by the use of a generally annular burner ring which circumscribes the pipes at their confronting ends. The ring has a number of radially inwardly directed burner jets or nozzles through which a combustible oxyacetylene flame is directed to the joint to be welded.
Most pipes, particularly those on lengthy pipe lines, are welded in place, and consequently are welded in a horizontal position. Application of heat to the circumferential joint thus presents a problem because of the fact that heat rises, so that even though one attempts to apply uniform heat around the pipe ends, the lower or under portion of the pipes will be brought to an elevated temperature faster than the upper portions of the pipes, and an undesirable temperature gradient is produced from bottom to top of the pipes.
It has been suggested that this problem can be overcome by providing different jet openings and/or spacing between adjacent jets or nozzles so that a greater amount of heat will be applied to the otherwise cooler upper portions of the pipes. This is not only far more expensive than providing a simple ring with standard size jet nozzles, but also presents substantial engineering design problems which vary according to the diametrical size of the pipes being welded.